Port fuel direct injection (PFDI) engines are capable of advantageously utilizing both port injection and direct injection of fuel. For example, at higher engine loads, fuel may be injected into the engine using direct fuel injection, thereby improving engine performance (e.g., increasing available torque and fuel economy). At lower engine loads, fuel may be injected into the engine using port fuel injection, thereby reducing vehicle emissions, noise, vibration, and harshness (NVH), and wear of the direct injection system components, (e.g., injectors, DI pump solenoid valve, and the like).
In addition, in order to provide desired catalyst performance and reduced emissions, PFDI engine air-fuel ratio may be maintained at a desired level (e.g., stoichiometric ratio). Typical feedback air-fuel ratio control may include monitoring of exhaust gas oxygen concentration by one or more exhaust gas sensor and providing feedback on air-fuel ratio errors in the engine, such that the amount of fuel delivered is continuously corrected based on the feedback from the exhaust sensors. In PFDI engines, the error in air-fuel ratio may be contributed by the fuel injection system components, such as components of port and/or direct fuel injection systems. By identifying the fueling error contribution from each fuel injection system (e.g., port or direct fuel injection systems), appropriate fueling corrections may be provided and therefore, any deviation in the air-fuel ratio may be promptly corrected. As a result, catalytic converter efficiency and engine performance can be improved.
Diverse approaches may be used to identify the source of fueling errors (e.g., port or direct fuel injection systems) in PFDI systems. One example approach is shown by Surnilla et al. in U.S. Pat. No. 9,631,573 wherein a non-intrusive fuel system calibration routine is provided to identify fueling errors for each of the two fuel injection systems. The approach determines fueling errors based on a rate of change of an air-fuel ratio with respect to a change in fuel fraction of each fuel injection system at different engine operating conditions. Further, the fueling error of one fueling system may be differentiated from the error of the other fueling system by allocating distinct portions of an air-fuel ratio error to each fueling system based on the corresponding fuel fractions delivered by them.
The inventors herein have identified potential issues with the above approach. Specifically, the approach of Surnilla may be able to detect and differentiate air-fuel ratio errors associated with each fuel injection system only when the change in fraction of fuel injected by each fuel injection system is sufficiently large and/or when the injected fuel mass is significantly large. At lower injection fuel masses and smaller changes in fuel fraction, even if a total air-fuel ratio error is determined, it may be difficult to parse out the error contribution of each injection system. Even if the error is parsed out, the confidence factor of the learned error may be lower. For example, a more accurate estimation of the error may be achieved when the fuel fraction ratio of the direct injection system: port injection system is 20%:80% as compared to 40%:60%. Further, since the fueling error is identified non-intrusively, there may be limited injection events where the injection fuel mass and/or change in fuel fraction is sufficient to provide reliable test results. If injection fuel mass and/or change in fuel fraction is intrusively changed to provide the required test conditions, vehicle drivability may be affected. As yet another example, the purging of a fuel vapor canister of the fuel system may be delayed until the calibration is completed to reduce air-fuel ratio excursions caused by the purging. As such, if the canister is not purged often enough, the canister may be unable to accommodate further fuel vapors, causing emissions to be degraded. The issue may be exacerbated in hybrid vehicles where lower engine run times already limit canister purging opportunities.
The inventors herein have recognized that a measurable change in air-fuel ratio may be provided by intrusively adjusting the fuel fraction provided by each fuel injection system while maintaining the fuel fractions within an upper and lower fuel fraction limit selected for each injection system as a function of engine operating conditions. By intrusively adjusting the fuel fractions of each fuel injection system, a sufficient change in each fuel injector fuel fraction may be provided to enable a reliable detection and differentiation of air-fuel ratio error via the approach of the non-intrusive calibration routine to be implemented. In one example, fueling errors in PFDI systems may be learned by a method for an engine comprising: delivering fuel in a cylinder cycle via a direct and a port injector; increasing a direct injection fuel fraction to an upper limit when a current fraction is closer to a lower limit than the upper limit; and decreasing the first fuel fraction provided by the direct injector to the lower limit when the current fraction is closer to the upper limit than the lower limit. In this way, the source of fueling errors may be reliably identified and addressed in a timely manner.
As one example, an initial fuel fraction value may be opportunistically learned and adapted via a non-intrusive fuel calibration routine. Responsive to a predetermined amount of time having elapsed since the last (non-intrusive) fuel adaptation, an intrusive routine may be initiated. Therein, upper and lower fuel fraction limits for each fuel injection system may be determined based on engine speed-load conditions, for example. The upper and lower limits may be selected such that a significant change in fuel fraction can be achieved without degrading vehicle drivability. The controller may then compare the previously adapted fuel fraction value to the upper and lower limits, and select a fuel fraction to apply on the current adaptation based on a distance of the previously adapted fuel fraction value from each of the corresponding upper and lower limits. For example, if the previously adapted fuel fraction value of the direct injection system is determined to be further away from the upper limit, then on the current adaptation, the upper limit fuel fraction value may be applied to the direct injection system. Else, if the previously adapted fuel fraction value of the direct injection system is determined to be further away from the lower limit, then on the current adaptation, the lower limit fuel fraction value may be intrusively applied to the direct injection system. In one example, the previous non-intrusive adaptation may have been performed with 40% direct injection and 60% port injection. During the subsequent intrusive adaptation, the upper and lower limits for direct injection may be determined to be 80% and 20%. Accordingly, the intrusive adaptation may be performed with 80% direct injection and 20% port injection and the previously learned air-fuel ratio error may be updated based on the most recently learned air-fuel ratio error.
In this way, by adjusting a fuel fraction applied to each fuel injection system based on dynamically selected upper and lower limits, a significant change in fuel fraction may be provided by each injection system. The technical effect of actively providing a significant change that is constrained by predefined limits is that a fuel system calibration may be implemented wherein fueling errors may be learned with a higher confidence value. Further, by enabling the intrusive fuel fraction adaptation to be enabled only when fuel trimming is required, the engine may be operated at the desired/pre-calibrated fuel fraction value as much as possible. In addition, the amount of time required for fuel adaptation may be reduced without compromising the accuracy of the fuel adaptation, enabling more frequent fuel canister purging. By improving canister purging frequency, emissions issues are reduced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.